A horizontal-shaft type system has been common in a conventional high-altitude wind power generation system, which includes a buoyant apparatus such as an aerostat or a balloon; a horizontal shaft substantially parallel with a flowing direction of fluid, i.e., winds from the front while hanging on the buoyant apparatus; and radial blades coupled to the horizontal shaft and rotating like an air vane with respect to the horizontal shaft. For example, Korean Patent Official Gazette (with publication No. 10-2011-0108485, published on Oct. 6, 2011) discloses the horizontal-shaft type wind power generation system (see FIG. 1 of the official gazette).
However, such a conventional horizontal-shaft type has to be unavoidably mounted with the blades having a large radius in order to produce power as required. Due to the blades having the large radius, the conventional horizontal-shaft type has problems that a structure for mounting the blades to the buoyant apparatus is complicated and the whole system is increased in volume and weight.
Also, the conventional horizontal-shaft type mostly has a structure that the blades are rotated at high velocity as being opened at the ends thereof, and therefore the blades having the large radius may hit the buoyant apparatus or the like danger of safety accidents may increase while the system operates at a high altitude.